The invention relates to a method of manufacturing a scanning device comprising a support for an information carrier, a motor for rotating the support about an axis of rotation, a scanning unit for scanning the information carrier and a displacement device for displacing the scanning unit relatively to the information carrier, according to which method the motor and the displacement device are each provided on a separate frame, and the scanning device is provided with a pretensioning means and an adjusting device, both frames being maintained at a mutual distance in at least one adjustment position, viewed in a direction parallel to the axis of rotation, under the influence of a pretensiohing force of the pretensioning means, and said distance being adjusted by means of the adjusting device.
The invention also relates to a scanning device manufactured in accordance with a method according to the invention.
A method of the type mentioned in the opening paragraph is generally known and customary, and is used, for example, in the manufacture of an optical scanning device comprising an optical scanning unit for scanning an optically scannable information carrier, such as a CD or DVD, by means of a laser beam. Particularly in the case of optical scanning devices for scanning information carriers with a high information density, an angular deviation between a laser beam path of the scanning unit and a normal to an information surface of the information carrier should lie within relatively small limiting values. Such an angular deviation develops during the manufacture of the scanning device as a result of manufacturing tolerances. To correct said angular deviation in the course of the manufacturing process, i.e. after the assembly of the scanning device, said scanning device is provided, in accordance with the known method, with an adjusting device in three adjustment positions, said three adjustment positions being mutually triangularly arranged around the motor and the axis of rotation, viewed in a plane extending transversely to the axis of rotation. Each of said three adjusting devices comprises a screw which is screwed into a screw hole extending substantially parallel to the axis of rotation, which screw hole is provided in the frame on which the motor with the support is provided. The screw is provided with a head which, under the influence of the pretensioning force exerted by the pretensioning means, supports the frame on which the displacement device with the scanning unit is provided. By rotating the three screws, the frame on which the displacement device with the scanning unit is provided can be oriented with respect to the frame on which the motor with the support are provided, and hence an orientation of the laser beam path with respect to the support can be adjusted. In particular, the support can be tilted with respect to the laser beam path about two tilt axes extending perpendicularly to the axis of rotation, and the support can be displaced in a direction parallel to the axis of rotation. After the mutual orientation of the laser beam path and the support has been thus adjusted, the frames are held in position with respect to each other in that the frame of the displacement device rests, under the influence of the pretensioning force exerted by the pretensioning means, against the heads of the three screws screwed into the frame of the motor. In this manner, a necessary possibility of adjusting the orientation of the laser beam path with respect to the support is obtained in a very practical and simple manner, and the orientation of the laser beam path is very accurately adjustable with respect to the support.
A drawback of the known method resides in that both frames are not stably held in position with respect to each other under the influence of said pretensioning force, particularly in the case of scanning devices wherein information carriers, such as a CD-ROM or a DVD-ROM, are rotated about the axis of rotation at a relatively high speed. As a result of imbalance forces, which are generally caused, at such high speeds of rotation, by imbalance of the information carrier, mutual displacements of the two frames counter to said pretensioning force occur at the location of the adjusting devices, resulting in undesirable deviations of the orientation of the laser beam path with respect to the information carrier.
It is an object of the invention to provide a method of the type mentioned in the opening paragraph, by means of which the orientation of the laser beam path with respect to the support can also be readily and accurately adjusted, in the course of the manufacture of the scanning device, and by means of which also the above-mentioned drawback of the known method can be precluded as much as possible.
To achieve this object, a method in accordance with the invention is characterized in that an amount of an adhesive is provided between the two frames at a location near the adjusting device, the adjusted distance between the two frames being secured by curing the adhesive provided between the two frames. The adhesive is provided in uncured form between the two frames during the mutual assembly of the frames. Preferably, use is made of an adhesive which has a relatively long curing time or which can be cured in a controlled manner using, for example, UV-light, so that the uncured state of the adhesive is maintained during the assembly and adjustment of the orientation of the frames with respect to each other. By virtue thereof, the mutual orientation of the frames can be adjusted, after assembly, by means of the adjusting device in a relatively simple and accurate manner comparable to the known method wherein the still uncured adhesive is deformed between the frames. The adjusted mutual orientation of the frames is subsequently secured by curing the adhesive, resulting in a so-called constrained securing. It has been found that the mutual orientation of the frames is thus very stably secured, so that the above-mentioned mutual displacements of the two frames under the influence of imbalance forces are substantially completely precluded. By using the above-mentioned adhesive, said securing is thus obtained in a very simple, practical and efficient manner.
A particular embodiment of a method in accordance with the invention is characterized in that the amount of adhesive is provided in an interspace between the adjusting device and the pretensioning means. By providing the adhesive in said interspace, the adjusted mutual orientation of both frames is secured in a very stable manner. If the pretensioning means comprises a mechanical spring, a receiving space is formed between the mechanical spring and both frames, wherein excess adhesive is efficiently received during adjusting the mutual orientation of both frames.
A further embodiment of a method in accordance with the invention is characterized in that said distance is adjusted by rotating a screw of the adjusting device, which screw is screwed into a screw hole of a first one of the two frames, which screw hole extends substantially parallel to the axis of rotation, and which screw is provided with a head against which a second one of the two frames rests under the influence of the pretensioning force, a further amount of adhesive being provided in the screw hole, and the screw being secured, after adjusting said distance, in the screw hole by curing the adhesive provided in the screw hole. In this further embodiment of a method in accordance with the invention, between the two frames preferably a same type of adhesive is used as in the screw hole of the adjusting device. The adjusted mutual orientation of the two frames can thus be secured in a very simple manner because the provision of a quantity of adhesive between the two frames in addition to the provision of a quantity of adhesive of the same type in the screw hole requires relatively little time and effort.
A scanning device in accordance with the invention, which is manufactured in accordance with a method according to the invention, is characterized in that the scanning device is provided with an adjusting device in three adjustment positions, a first one and a third one of the adjusting devices being arranged, on a Y-axis, so as to be diametrically opposed, with respect to the axis of rotation, said Y-axis extending perpendicularly to the axis of rotation, and a second one of the adjusting devices being arranged on a X-axis extending perpendicularly to the axis of rotation and the Y-axis, while the first, the second and the third adjusting device are provided with, respectively, a first, a second and a third cylindrical guide sleeve, which are provided on the first frame and each comprise the screw hole of the relevant adjusting device, and with, respectively, a first, a second and a third cylindrical supporting element, which are provided on the second frame and are guided around, respectively, the first, the second and the third guide sleeve, the second frame resting against the heads of the screws of the three adjusting devices through the help of three supporting elements and under the influence of the pretensioning force. The cylindrical guide sleeves and the cylindrical supporting elements each have two functions, namely guiding the first frame with respect to the second frame during adjusting the mutual orientation of the two frames, and, respectively, supporting the screw holes of the adjusting devices and making the second frame bear against the heads of the screws of the adjusting devices, so that a very practical construction of the scanning device is obtained. Both frames can be mutually tilted about said Y-axis and said X-axis by a rotation of, respectively, the screw of the second adjusting device and the screws of the first and the third adjusting device. Both frames can be mutually displaced in a direction parallel to the axis of rotation by rotating the screws of each one of the three adjusting devices.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.